1. Field of the Invention
The present invention relates to the field of semiconductor fabrication and processing and more particularly to low utilization processes accomplished by decoupled plasma nitridation, rapid thermal processing, and chemical vapor deposition.
2. Discussion of Related Art
Low species utilization processes include the diffusion of nitrogen into silicon dioxide gate dielectric layers by decoupled plasma nitridation (DPN), the deposition of a silicon dioxide film by rapid thermal processing (RTP) or chemical vapor deposition (CVD), and the deposition of silicon epitaxial layers by CVD. In each of these low species utilization processes it is valuable to obtain a diffusion of atoms or a thin film that is very uniform across the substrate on which the process is performed. This is because as devices are further scaled down, they require thinner films and lower concentration diffusion of atoms into a substrate. Thinner films and lower concentration diffusion of atoms into a substrate in turn require that the variation in film thickness or diffusion concentration across a substrate be insignificant.
Nitride diffusion into a silicon dioxide gate dielectric may be performed in a decoupled plasma nitridation (DPN) chamber. Nitrogen gas is flowed into the chamber containing the substrate on which the silicon dioxide gate dielectric is formed and a plasma is struck while the flow continues. The plasma ionizes the nitrogen and the ionized nitrogen then diffuses into the silicon dioxide gate dielectric.
The formation of a silicon dioxide film by rapid thermal processing (RTP) may be performed in an RTP chamber. Hydrogen (H2) and oxygen (O2) gas is flowed into the RTP chamber and a silicon substrate is heated up to a temperature at which the hydrogen and oxygen gases react with the silicon substrate to form a silicon dioxide layer.
The formation of an epitaxial layer by chemical vapor deposition (CVD) may be performed in a CVD chamber. A precursor gas of the type of material to be deposited is flowed into the chamber, often along with a carrier or diluent gas. The chamber is heated to a temperature at which the precursor gases react to form a vapor and form a film on a substrate while the gas is flowed through the chamber.
Throughout each of these processes, gas is flowed through the chamber and the pressure within the chamber may be different in different parts of the chamber. The pressure gradients may be due to the constant flow of gases into the chamber and the flow of gases pumped out of the chamber. These flow and pressure gradients may be a primary factor in causing nonuniformity across a substrate of the amounts of atoms diffused into the substrate or of the thickness of a film formed on the substrate.
Several modifications to the reaction chambers have been made to reduce the nonuniformity caused by flow and pressure gradients. These modifications include pumping plates, gas distribution plates, and showerheads. Pumping plates are designed to control the flow and pressure gradients caused by the flow of gas into and out of the chamber. Gas distribution plates are designed to evenly distribute gas throughout the chamber to overcome non-uniform distribution of gas caused by the flow and pressure gradients. Showerheads are designed to distribute the gas flowed into the chamber in a particular way to overcome the flow and pressure gradients.
These modifications to the reaction chambers can help reduce pressure and flow gradients created by the flow of gases from the supply to the pump. But, these modifications do not provide enough uniformity for processes, and in particular low utilization processes where the consumption of the reactant is relatively insignificant.